i don't think there's any question how the obama administration will come down on it. >> we move on. >> yes, we do. >>> as we mentioned, president obama appeared at the white house briefing room last night. he thanked authorities and said many unanswered questions remain. nbc's kristen welker is there this morning. kristen, good morning to you. >> all in all this has been a tough week. >> reporter: in a late-night appearance in the white house briefing room, president obama praised the quick work of the fbi, state and local officials who brought an end to five days of terror. >> and tonight because of their determined efforts we've closed an important chapter in this tragedy. >> reporter: administration officials say fbi director robert mueller broke the news to the president that federal agents had arrested the second suspect. homeland security adviser lisa monaco also briefed the president. >> how did they plan and carry out these attacks and did they receive help? >> reporter: the comments cap an extraordinary day which saw the boston area go into lockdown mode hours after the pre